The present invention relates to polymeric binding elements adapted for permanently binding apertured stacks of paper.
U.S. Pat. No. 3,596,929 and my U.S. Pat. No. 3,970,331 describe two different types of inexpensive molded polymeric binding elements presently in use for permanently binding together apertured stacks of paper. Both comprise a first binding strip from which project a plurality of spaced studs adapted to be positioned through the apertures in the stack with the first binding strip adjacent one surface of the stack, and a second binding strip having spaced openings adapted to freely receive the studs. The second binding strip can be positioned over and locked in engagement with the ends of the studs projecting beyond the apertured stack of sheets to bind the stack. The studs of the binding element described in U.S. Pat. No. 3,596,929 are locked in engagement with the second strip by heat forming enlarged heads on the studs, whereas the studs on the binding element described in my U.S. Pat. No. 3,970,331 are locked to the second strip by pressing blocks into the openings to engage ratchet teeth on the studs with teeth on the second strip projecting into the openings.
The device required for forming heads on the studs of the binding element described in U.S. Pat. No. 3,596,929 includes electrical heaters which must be specially protected to prevent a fire hazard, particularly in the presence of paper chaff where, as has been done, the heating and forming device is combined with a machine for punching apertures in a stack of paper (see U.S. Pat. No. 3,756,625). Also the device can only be used where a source of electrical power is available.
While the binding element described in my earlier U.S. Pat. No. 3,970,331 can be attached to a stack of paper by an entirely mechanical device, thereby eliminating the problems associated with electrical heaters (see my U.S. Pat. No. 3,879,783), the mold required to form the ratchet teeth on the binding element is more complex than might otherwise be desired.